In some cases ,WEB API It may take a long time to process the request , It is not feasible for the client to wait for the work to be completed , For example, connection timeout, etc .

At this time , have access to “ asynchronous Request-Reply Pattern ”.

asynchronous Request-Reply Pattern

asynchronous Request-Reply Pattern means ： When the back-end processing needs to be asynchronous, but the front-end still needs a clear response , Separate the back-end processing from the front-end .

The overall process is as follows :

• Client applications for business API To call , Trigger long-running operations on the back end ;

• API Return the response immediately . return HTTP 202 Accepted ( Accept ) Status code , Confirm that the request has been received for processing , The response contains a header , Contains the status that the client can poll API Address , To check the results of long-running operations ;;

• The client polls this status API, If the operation is not completed , Then return to HTTP 202, Otherwise return to HTTP 200, And include the actual response data .

Now let's demonstrate how to do it in ASP.NET Core To realize .

Demo

We use waiting 20 Second simulates a long time API operation ：

[HttpGet]
[Route("get")]
public async Task<IEnumerable<WeatherForecast>> Get()
{
    await Task.Delay(20000);
    var rng = new Random();
    return Enumerable.Range(1, 5).Select(index => new WeatherForecast
    {
        Date = DateTime.Now.AddDays(index),
        TemperatureC = rng.Next(-20, 55),
        Summary = Summaries[rng.Next(Summaries.Length)]
    })
    .ToArray();
}

First , We create a new API operation ：

[HttpGet]
[Route("async/get")]
public async Task<IActionResult> AsyncGet()
{
    string id = Guid.NewGuid().ToString();
    string responseValue = [email protected]"/status/{id}";

    _cache.SetString(id, responseValue);

    Task.Factory.StartNew(() =>
    {
        var result = Get().Result;
        _cache.SetString(id + "_result", JsonConvert.SerializeObject(result));
    });
    
    return Accepted(responseValue);
}

The specific function is to hand over a long time to Task perform , The execution results will be put into the distributed cache , Then return to HTTP 202 Accepted.

The client no longer accesses the original request address , Instead, use this new address ：

then , We create a state API For polling ：

[HttpGet]
[Route("/status/{id}")]
public IActionResult Status(string id)
{
    var result = _cache.GetString(id + "_result");
    if (!string.IsNullOrEmpty(result))
    {
        return Ok(result);
    }

    return Accepted(_cache.GetString(id));
}

Client according to ID Poll .

When the operation is not completed , Keep going back HTTP 202：

When the operation is complete , Return the results in the distributed cache ：

Conclusion

If your API There are long-running operations , The polling information should be returned to the caller as soon as possible , So that they can check the progress .

Want to know more about , Please pay attention to my official account ”My IO“